KR20080082737A - Apparatus and method quadrature modulation in communication system - Google Patents

Abstract

A quadrature modulation apparatus in a communication system and a modulating method thereof are provided to compensate for an output signal deterioration of a modulator actively according to a circumference environment. A quadrature modulation apparatus in a communication system includes DC offset adjusting units(204,206), a quadrature modulator(220), a switch(230), a power detector(260), and a DC offset calculation unit(280). The DC offset adjusting units adjusts a DC offset of I-channel and Q-channel signals. The quadrature modulator performs a quadrature modulation for the I-channel and Q-channel signals using a local oscillation signal. The switch switches an output signal of the quadrature modulator to a main signal path or a compensation path. The power detector is configured in the compensation path, detects a power of the local oscillation signal from an output signal of the switch, and detects a power of the detected local oscillation signal. The DC offset calculation unit generates a DC offset adjusting value to the DC offset adjusting units, and finds a minimum power value by analyzing power values of the power detector. The DC offset calculation unit determines a DC offset value corresponding to the minimum power value as an optimum value.

Description

Apparatus and method for orthogonal modulation in communication system {APPARATUS AND METHOD QUADRATURE MODULATION IN COMMUNICATION SYSTEM}

1 is a diagram showing the configuration of a transmitter in a TDD system according to the prior art.

2 is a diagram illustrating a configuration of a transmitter in a TDD based communication system according to an embodiment of the present invention.

3 is a diagram illustrating an operation procedure for minimizing LO feedthrough in a transmitter using an orthogonal modulator according to an embodiment of the present invention.

4 is a graph showing the relationship between DC offset and LO feedthrough in accordance with the present invention.

The present invention relates to an apparatus and method for minimizing LO feedthrough of an orthogonal modulator in a communication system, and more particularly, to an apparatus and method for automatically optimizing the input DC offset of an orthogonal modulator through a correction path in a communication system. It is about

In general, a duplexing scheme of a wireless communication system can be largely divided into a frequency division duplex (FDD) scheme and a time division duplex (TDD) scheme. The FDD scheme includes an uplink and a downlink. A communication method is performed using different frequency bands, and the TDD method is a method in which uplink and downlink communicate using different time bands.

In particular, the TDD scheme can be supported at the same transmission rate using fewer time slots than the FDD scheme, and is suitable for transmission of an asymmetric or bursty application due to dynamic allocation of time slots. As a result, it is being researched and developed with very attractive technology for telecommunication operators who want to provide inexpensive wireless Internet service.

1 shows a configuration of a transmitter in a TDD system according to the prior art.

The configuration mainly converts a digital signal into an analog signal and then converts the signal into an RF signal, and includes a digital / analog converter 100, a local oscillator 102, an orthogonal modulator 102, and a bandpass filter 104.

Referring to FIG. 1, first, the digital-to-analog converter 100 converts an input digital signal into an analog signal. The signals output from the digital-to-analog converter 100 are I (inphase) channel signals and Q (Quadrature) channel signals, and each channel signal is a differential signal as shown. That is, the I_p signal and the I_n signal are output for the I channel, and the Q_p and Q_n signals are output for the Q channel.

The local oscillator 102 generates a local oscillator (LO) frequency for converting an intermediate frequency (IF) signal or a baseband signal to a radio frequency (RF) signal. Quadrature modulator 104 converts the I-channel and Q-channel signals from the digital-to-analog converter 100 with the local oscillation frequency signals from the local oscillator 102 and converts them into RF band signals and converts them into the RF band. The added I-channel signal and Q-channel signal are added and output.

The band pass filter 106 passes only the signal of a desired band and outputs the signal from the quadrature modulator 104. The signal output from the bandpass filter 106 is amplified by a power amplifier (not shown) and then transmitted through an antenna.

The transmitter using the IQ modulator 104 as shown in FIG. 1 applies a direct current (DC) voltage to the IQ input terminal in consideration of the characteristics of the modulator in a circuit configuration. As described above, the IQ modulator using the fixed DC voltage has a problem in that the transmission signal is degraded because there is no way to compensate for the LO feedthrough change due to temperature change or power level change of the IQ input signal. In other words, in order to minimize the LO feedthrough, the DC offset of the differential signals I_p and I_n, Q_p and Q_n input to the quadrature modulator 104 should be optimized according to the current state. It is also possible to check the LO feedthrough by manually changing the DC voltage applied to the IQ input terminal, which is a difficult and cumbersome problem with manual operation.

It is therefore an object of the present invention to provide an apparatus and method for automatically optimizing a DC voltage applied to an input terminal of a quadrature modulator in a communication system.

Another object of the present invention is to provide an apparatus and method for minimizing local oscillator (LO) feedthrough in a communication system.

Another object of the present invention is to provide an apparatus and method for optimizing a DC voltage applied to an input terminal of a quadrature modulator through a calibration path during a reception period in a TDD-based communication system.

According to an aspect of the present invention for achieving the above object, in the transmitter device in the communication system, an adjustment unit for adjusting the DC offset of the I-channel and Q-channel signal which is a differential signal, the I-channel and Q with the DC offset is adjusted An orthogonal modulator for orthogonally modulating a channel signal using a local oscillator (LO) signal, a switch for switching the output signal of the orthogonal modulator to a main signal path or a correction path, and the correction path; Detects a local oscillation signal in the signal of the signal, and generates a DC offset adjustment value to the detection unit for detecting the power of the detected local oscillation signal, the adjustment unit, and analyzes the power values from the detection unit to find the minimum power value, And a calculator configured to determine a DC offset value corresponding to the minimum power value as an optimal value.

According to another aspect of the present invention, in a method of minimizing local oscillator (LO) feedthrough in a communication system, in a correction mode, a DC offset of an I channel or a Q channel signal input to an orthogonal modulator is adjusted according to a predetermined rule. A process of detecting a local oscillation signal from an output signal of the quadrature modulator, a process of detecting power of the detected local oscillation signal, and a process of searching for a minimum power value by analyzing the detected power values And determining a DC offset value corresponding to the minimum power value as an optimal value.

Hereinafter, the operating principle of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

Hereinafter, the present invention will propose a method for automatically optimizing the DC voltage applied to the input terminal of the quadrature modulator in a communication system.

In the following description, a TDD-based communication system is described as an example, but the same may be applied to a communication system of another duplexing method such as FDD. If a system continuously transmits a signal such as an FDD system, a separate correction time interval may be provided to optimize a DC voltage applied to an input terminal of a quadrature modulator.

2 illustrates a configuration of a transmitter in a TDD based communication system according to an embodiment of the present invention.

The configuration mainly converts a digital signal into an RF signal and then converts the signal into an RF signal. The digital / analog converter 200, the local oscillator 210, the quadrature modulator 220, the switch 230, and the first band pass filter 240, a second band pass filter 250, a power detector 260, an analog / digital converter 270, and a DC offset calculator 280. According to the present invention, the control unit 202 and the DC offset adjusting units 204 and 206 in the digital-to-analog converter 200 are configured.

First, referring to an operation when a signal is actually transmitted, the digital-to-analog converter 200 converts an input digital signal into an analog signal. The signals output from the digital-to-analog converter 100 are I (inphase) channel signals and Q (Quadrature) channel signals, and each channel signal is a differential signal as shown. That is, the I_p signal and the I_n signal are output for the I channel, and the Q_p and Q_n signals are output for the Q channel. At this time, the DC offset adjusting units 204 and 206 apply a predetermined DC voltage as the I channel and Q channel signals under the control of the controller 202.

The local oscillator 210 generates a local oscillator (LO) frequency for converting an intermediate frequency (IF) signal or a baseband signal to a radio frequency (RF) signal. Quadrature modulator 220 converts the I-channel and Q-channel signals from the digital-to-analog converter 200 with the local oscillation frequency signals from the local oscillator 210 to convert them into RF band signals and convert them into the RF band. The added I-channel signal and Q-channel signal are added and output.

The switch 230 switches the output signal of the quadrature modulator 220 to the main signal path in the transmission section by the TDD control signal from the DC offset calculator 280, and in the reception section. The output signal of the quadrature modulator 220 is switched to a cal path.

The first band pass filter 240 passes only the signal of the transmission band and outputs the signal from the switch 230. The signal output from the first band pass filter 240 is amplified by a power amplifier (not shown) and then transmitted through an antenna.

Next, referring to the operation during the reception period, the DC offset calculator 280 provides the DC offset adjustment value to the controller 202 to find an optimal DC offset (or LO feedthrough). Then, the controller 202 controls the DC offset adjusters 204 and 206 according to the DC offset adjust value. DC offset correction is performed sequentially for the I channel and the Q channel, and since the correction operation is the same, the following description will focus on the correction operation for the I channel.

The DC offset adjusting unit 204 adjusts the DC offset of the I channel signals I_p and I_n input to the quadrature modulator 220 under the control of the control unit 202. The quadrature modulator 220 orthogonally modulates the I-channel signal and the Q-channel signal from the digital-to-analog converter 200 using the local oscillation frequency signal from the local oscillator 210 and outputs the quadrature modulated signal. Since the switch 230 is a reception section, the switch 230 switches the output signal of the quadrature modulator 220 to a correction path.

The second band pass filter 240 outputs only the signal of the LO frequency band from the signal from the switch 230. The power detector 260 detects and outputs the power of the signal from the second band pass filter 240. The analog / digital converter 270 converts the analog signal from the power detector 260 into a digital signal and outputs the digital signal.

The DC offset calculator 280 compares and analyzes the LO feedthrough values (power detection values) according to the DC offset adjustment, and provides the controller 202 with a DC offset value at which the LO feedthrough is minimal. . If it is determined that the DC offset adjustment is necessary continuously, the DC offset calculator 280 changes the DC offset value by a predetermined value, and provides the changed value to the controller 202 to continue the correction operation. Proceed. The DC offset calculator 280 may be implemented as a field-programmable gate array (FPGA). Meanwhile, the operation of finding an optimal DC offset value may be performed for at least one frame period.

3 illustrates an operation procedure for minimizing LO feedthrough in a transmitter using an orthogonal modulator according to an embodiment of the present invention. In particular, Figure 3 shows in detail the operation corresponding to the calibration path (calibration path) according to the present invention. Both the I channel and the Q channel adjust the DC offset through the algorithm as shown in FIG. 3. Hereinafter, the I channel will be described as an example.

Referring to FIG. 3, in step 301, the transmitter initializes the DC offset value of the I channel to '0' and detects the power of the LO signal in the correction path. That is, the initial power measurement for the leakage LO signal is performed without adjusting the DC offset. Here, the DC offset refers to the difference of the DC voltage level between I_p and I_n. In operation 303, the transmitter adjusts the DC offset value to be larger by a first value Vstep. In operation 305, the transmitter detects an LO signal in a correction path and detects power of the detected LO signal. In other words, an LO signal is detected by bandpass filtering the output signal of the quadrature modulator, and the power of the detected LO signal is measured.

In step 307, the transmitter compares the detected current power value with the immediately previous detected power value. Here, the previously detected power value represents the power value of the LO signal detected at the time of the previous DC offset adjustment. If the current power value is less than or equal to the previous power value, the transmitter continues to return to step 303 to perform a subsequent step again to adjust the DC offset value largely.

If the current power value is greater than the previous power value during the repeating loop, the transmitter proceeds to step 309 and adjusts the current DC offset value to be smaller by a second value (eg, 2Vstep). After adjusting the DC offset value to small, the transmitter proceeds to step 311 to detect the LO signal in the correction path and to detect the power of the LO signal.

In step 313, the transmitter compares the detected current power value with the immediately detected power value. If the current power value is less than or equal to the previous power value, the transmitter returns to step 303 to perform the following steps again to adjust the DC offset value to be large. On the other hand, if the current power value is greater than the previous power value, the transmitter proceeds to step 315 to determine the immediately previous DC offset value as the optimal DC offset value.

In the subsequent transmission, the transmitter controls the DC offset of the I channel input to the quadrature modulator using the optimal DC offset value.

4 is a graph showing the relationship between DC offset and LO feedthrough in accordance with the present invention.

The present invention observes the LO feedthrough (power value of the leakage LO signal) while adjusting the DC offset value large or small, and determines the optimal DC offset value a that the LO feedthrough is determined to be the minimum.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

As described above, the present invention has an advantage in that the transmitter using the quadrature modulator can actively compensate for the deterioration of the output signal of the modulator due to changes in the surrounding environment, such as temperature change and level change of the IQ input signal. In particular, the present invention has the advantage that it is possible to configure a correction path without adding a separate device using the features of the TDD system.

Claims (12)

A transmitter apparatus in a communication system, Adjusting unit for adjusting the DC offset of the differential signal I channel and Q channel signal, An orthogonal modulator for orthogonally modulating the I and Q channel signals with the DC offset adjusted using a local oscillator (LO) signal; A switch for switching the output signal of the quadrature modulator to a main signal path or a correction path; A detection unit configured in the correction path, for detecting a local oscillation signal from a signal from the switch, and detecting a power of the detected local oscillation signal; And generating a DC offset adjustment value to the adjustment unit, analyzing a power value from the detection unit, finding a minimum power value, and determining a DC offset value corresponding to the minimum power value as an optimal value. Device. The method of claim 1, wherein the detection unit, A bandpass filter for passing only a local oscillation frequency band in the signal from the switch; A power detector for measuring the power of the signal from the bandpass filter; And an analog / digital converter for converting the signal from the power detector into a digital signal. The method of claim 1, In the case of a system based on Time Division Duplexing (TDD), the correction path is operated during a reception period. The method of claim 3, The operation of finding the optimal value is characterized in that is performed during at least one frame period. The method of claim 1, In the case of a TDD-based system, the switch switches the output signal of the quadrature modulator to the main signal path during the transmission period and the output signal of the quadrature modulator to the correction path during the receiving period. The method of claim 1, A band pass filter for passing only a signal of a transmission band in a signal from the switch; And a power amplifier for power amplifying the signal from the bandpass filter. The method of claim 1, And an analog / digital converter for converting a digital signal into an analog signal and generating the differential channel I and Q channel signals. In a communication system minimization method of LO (Local Oscillator) feedthrough, In the correction mode, adjusting the DC offset of the I-channel or Q-channel signal input to the quadrature modulator according to a predetermined rule; Detecting a local oscillation signal from an output signal of the quadrature modulator; Detecting power of the detected local oscillation signal; Searching for the minimum power value by analyzing the detected power values; Determining a DC offset value corresponding to the minimum power value as an optimal value. The method of claim 8, The correction mode, characterized in that performed in the reception period in the case of a TDD-based system. The method of claim 10, The finding of the optimal value is performed during at least one frame period. The method of claim 1, In the case of a TDD-based system, the output signal of the quadrature modulator is switched to the main signal path during the transmission period and to the correction path during the reception period. The method of claim 1, The I channel and Q channel signal is characterized in that the differential signal (differential signal).

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